xkcd #3135: Sea Level
Title text:
They're up there with coral islands, lightning, and caterpillars turning into butterflies.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3135/
Everyone was taught the tides look like two giant water bulges going around the earth in line with the moon.
That representation is oversimplified and false.
This is how the tides look like at a global level. It’s messed up.
Tides in the Bay of Fundy, Canada are 16 metres (50 feet).
See, that's the part that confuses the hell outta me. How can water be higher in one spot than others just due to the Moon's gravity? Yeah it's the geography of the area, got it. But still, how?
Ever seen a ferrofluid, which follows the shape of magnetic fields? Same thing, but with gravity.
Of course, that only accounts for a fraction of those 16 meters... but there's a lot of ocean water. Get it moving (because the Moon and the Sun move, and the Earth rotates under them, and there's a whole lot of ocean currents on top of that, due to differences in water temperatures and salinity, and coriolis forces, and winds, and whatnot) and it builds up a lot of inertia.
Push it into geography that keeps narrowing and narrowing like a funnel, and the only place it can go is in, and up.
Water gets in there, wants to get out, but there's a whole damn ocean pushing it in, so it has no option but to keep accumulating into the funnel.
Also, having the geography look a bit like a Tesla valve that'll easily let water in but not so easily let it out probably doesn't help either; place's bound to get close to overflowing, before it can empty itself out.
Imagine being out exploring new islands, not realizing its low tide. You setup camp for the night on an island that's relatively flat and close to current sea-level. Then while you're sleeping the tide comes in and washes your whole camp out to sea...
Come to the beach here in Bordeaux (well, on the coast) and see tourists set up their stuff at low ebb but forgetting they have to watch out for the flood.
if you are exploring islands you probably have a solid idea of how tides work.
You probably should, but that doesn't mean you do. It's not like anyone makes you take a quiz to go wander around outside.
Plenty of people get themselves into trouble all the time exploring places/things they know nothing about.
i lived near the beach for a while and, uh, i have seen tourists do the stupid. i posit they count.
"Their moon is tidally locked" is an absolutely metal thing to say about a planet.
I wonder if anyone has ever done the math on how much (in L or kg) water is moved by the moon each day. It's got to be something absurd.
Just wanted to mention I see your pfp on every post.
Thank you for keeping lemmy alive and making like 4% of the total posts. Seeing you post brightens up my day.
No homo.
Let's hope Lemmy grows big enough that I can just be part of the crowd.
I have to assume it's about one moon's worth, divided by the distance squared.
That would be its total pull, not just the water.
We probably can estimate the amount of water that's at a different level from what a moonless Earth would.
We could also say that technically all water is moved somewhat, because gravity is like that.
In the Bay of Fundy, Canada we have the highest tides in the world (53 feet high). It's enough to make some of the tributary rivers flow backward with the rising tide. I've seen it my whole life but it still amazes me to see a harbour completely empty of water with boats sitting on the bottom waiting for the tide to come back in.
I think lightning would be crazy to anyone who never experienced a planet with it. Like, "WTF, sometimes your sky does what?"
Nah, that's just Poseidon having a bad mood today. Just have to sacrifice your first child to make it stop for 10 years.
And when Mercury is in retrograde, you can make an excuse for anything being kind of shitty or off.
There better not be mercury in my Gatorade!
Y'see, that's not quite how it works.
No, no, no; We're just giving Mercury a retro-grade.
I'm thinking maybe a C to C+ at best. I mean it's kinda 'retro', but that's definitely not the first description that comes to mind.
Just scoop it off the top, jeez.
FlatEarthersSayWhat
They'll just say the moon pulls the water around as it circles above the flat disc or something idk
But the moon alone doesn't orbit at the same rate as the tides. Alternatively they are fucking morons and shouldn't be respected so who cares.
"The earth tilts when the moon hits far end of earth during moonset and that's why there is low tide. A high tide happens during moonrise when the moon drags it up slightly."
Thats just the tilting from where the elephants shrug
Well, tides on moons (eg around gassy supergiants :)) are fairly usual.
So perhaps it's not as much as the tides being "sci-fi" (sci??) but the relative size of Earth's Moon (it's basically a binary planet situation where they orbit around each other).
So, the sheer size of our moon as seen from the planet's surface is the rarity.
\
(Then again, on a moon around a supergiant the same experience could be had from one tiny beings pov.)
gassy supergiants
Ugh, there you go talking smack about my mamma again! Dammit, Evil Shrubbery!
Dense at the core, but what escapes is free for all the solar system to enjoy.
I live in an area with sea but almost no tide (although wind direction can have a pretty big effect on water level) and I have always felt that tides are weird man.
Yeah I grew up inland and tides are weird
woah XKCD is still making comics?
I remember never believing my parents when they explained it to me as a kid. Clouds being caused by cigarette smoke was reasonable but the moon pulling out the ocean seemed too outrageous.
As a child, my friend was told by her mother that wind occurs because people group up and blow really hard.
aw fuck. i missed a chance to say "people suck" when asked that. does anyone have a way to get me back to say 2012?
Does the moon decrease the air pressure enough for that to matter?